Turbine shroud cooling hole diffusers and related method

ABSTRACT

An inner shroud assembly for a turbine comprising a plurality of part-annular segments combining to form an inner, annular shroud adapted to surround rotating components of a turbine, each segment having a pair of end faces that are juxtaposed similar end faces on adjacent segments with gaps therebetween; at least one convection cooling hole in the segment, opening along at least one of the pair of end faces. The cooling hole opens specifically into a diffuser recess formed in one of the pair of end faces for diffusing the flow of cooling air into the gap.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to impingement cooling for a shroudassembly surrounding the rotating components in the hot gas path of agas turbine, and particularly relates to supplying purge air to the gapsbetween the inner shroud segments to cool the segments and to preventhot gas ingestion into the gaps.

[0002] Shrouds employed in a gas turbine surround and in part define thehot gas path through the turbine. Shrouds are typically characterized bya plurality of circumferentially extending shroud segments arrangedabout the hot gas path, with each segment including discrete inner andouter shroud bodies. Conventionally, there are two or three inner shroudbodies for each outer shroud body, with the outer shroud bodies beingsecured by dovetail-type connections to the stationary inner shell ofthe turbine and the inner shroud bodies being secured by similardovetail connections to the outer shroud bodies. The inner shroudsegments directly surround the rotating parts of the turbine, i.e., therotor wheels carrying rows of buckets or blades. Because the innershroud segments are exposed to hot combustion gases in the hot gas path,systems for cooling the inner shroud segments are oftentimes necessaryto reduce the temperature of the segments. This is especially true forinner shroud segments in the first and second stages of a turbine thatare exposed to very high temperatures of the combustion gases due totheir close proximity to the turbine combustors. Heat transfercoefficients are also very high due to rotation of the turbine bucketsor blades. To cool the shrouds, typically relatively cold air from theturbine compressor is supplied via convection cooling holes that extendthrough the segments and into the gaps between the segments to cool thesides of the segments and to prevent hot path gas ingestion into thegaps. The area that is purged and cooled by the flow from a singlecooling hole is small, however, because the velocity of the cooling airexiting the cooling hole is high, and the cooling air diffuses like ajet and flows into the hot gas flow path.

[0003] Previous design methods thus required multiple cooling holes inclose proximity to each other, using increased amounts of cooling airfrom the compressor (and additional machining) which, in turn, reducesthe efficiency of the turbine.

BRIEF SUMMARY OF THE INVENTION

[0004] In an exemplary embodiment of the invention, a cooling circuitfor purging cooling air into the gaps between inner shroud segmentsincludes convection holes that incorporate diffusers at their respectiveoutlet ends. Each diffuser may include an elongated, substantiallyrectangularly-shaped outlet recess or cavity with a cross-section thattapers away from (i.e., increases outwardly from) the respectiveconvection hole, terminating at the face of the segment. Morespecifically, the convection hole extends at an angle of about 45°relative to the segment face, opening into the diffuser recess near arearward or upstream end of the recess, relative to the direction ofpurge or cooling flow. The diffuser recess includes a long taperedportion extending in the flow direction (or forward of the convectionhole) and a short tapered portion extending in a direction opposite theflow direction. The end result is that the cooling or purge air beginsto diffuse before it reaches the face of the segment, enhancing thecooling of the segment edges. While the cooling or purge air does losesome velocity in the diffuser, sufficient pressure is maintained toprevent hot gas path gases from entering the gaps between the innershroud segments.

[0005] Accordingly, in its broader aspects, the invention relates to aninner shroud assembly for a turbine comprising a plurality ofpart-annular segments combining to form an inner, annular shroud adaptedto surround rotating components of a turbine, each segment having a pairof end faces that are juxtaposed similar end faces on adjacent segmentswith gaps therebetween; at least one convection cooling hole in the partsegment, opening along at least one of the pair of end faces; said atleast one cooling hole opening into a diffuser recess formed in one ofthe pair of end faces for diffusing the flow of cooling air into thegap.

[0006] In another aspect, the invention relates to a segment for aturbine shroud assembly comprising a segment body having a sealing faceand opposite end faces; and at least one convection cooling holeextending through the segment body and opening into a diffuser recessformed in a respective end face of the segment body.

[0007] In still another aspect, the invention relates to a method ofpurging cooling air into gaps between adjacent part annular segments ina turbine shroud assembly comprising a) supplying cooling air throughone or more cooling holes formed in each segment, each cooling holeopening along an end face of the segment; and b) diffusing the coolingair before it reaches the end face of each segment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a simplified partial section of a turbine inner shroudsegment located between a first stage bucket and a second stage nozzle,incorporating an inner shroud diffuser in accordance with the invention;

[0009]FIG. 2 is a horizontal section taken through the diffuser portionof the inner shroud segment shown in FIG. 1; and

[0010]FIG. 3 is a horizontal section similar to FIG. 2, but illustratingthe arrangement of a pair of diffusers in adjacent shroud segments.

DETAILED DESCRIPTION OF THE INVENTION

[0011] Referring now to FIG. 1, there is illustrated portions of ashroud system 10 surrounding the rotating components in the hot gas pathof a gas turbine. The shroud system 10 is secured to a stationary innershell of the turbine housing 12 and surrounds the rotating buckets orvanes 14 disposed in the hot gas path. The portions of shroud system 10shown in FIG. 1 are for the first stage of the turbine, and thedirection of flow of the hot gas is indicated by the arrow 16. Theshroud system 10 includes outer and inner shroud segments 20 and 22,respectively. It will be appreciated that the shroud system includes aplurality of such segments arranged circumferentially relative to oneanother with two or three inner shroud segments 22 connected to each oneof the outer shroud segments 20. For example, there may be on the orderof forty-two outer shroud segments circumferentially adjacent oneanother and eighty-four inner shroud segments circumferentially adjacentone another, with a pair of inner shroud segments being secured to anouter shroud segment, and with gaps between adjacent inner segments. Theindividual inner shroud segments that are of interest here aresubstantially identical, and thus only one need be described in detail.

[0012] The segment 22 includes a segment body 24 having a radially innerface 26 that mounts a plurality of labyrinth seal teeth, or acombination of labyrinth seal teeth, brush and/or cloth seals (notshown). Each segment body is formed with substantially identicalcircumferential end faces, one of which is shown at 28. Segment 22 ismounted to an outer shroud segment 20 by a conventional hook and C-cliparrangement at 32.

[0013] Cooling air from the turbine compressor is supplied viaimpingement cavity 34 that receives the cooling air through animpingement plate 35 to at least one convection hole 36 (one shown)drilled through the segment 22 and opening into a diffuser recess 38 atthe circumferential end face 28 of the segment. With specific referenceto FIG. 2, the diffuser recess includes an extended taper 40 in thedownstream or flow path direction, and a shorter and more sharply angledtaper 42 in the upstream or counter flow path direction, with the hole36 opening into the rearward portion of the recess, where tapers 40 and42 intersect. With this arrangement, cooling air flowing through thehole 36 will rapidly diffuse into the larger downstream portion of therecess 38 and then into the circumferential gap between adjacentsegments. The diffused cooling air thus convection cools a largerportion of the segment, and impingement cools a larger portion of theadjacent segment. At the same time, sufficient pressure is maintained toprevent any ingestion of hot gas path gases into the gap betweenadjacent segments.

[0014]FIG. 3 illustrates how adjacent convection holes 44, 46 andassociated respective diffuser recesses 48, 50 on adjacent segment faces52, 54 are juxtaposed, and supply cooling air into the gap 56 betweenthe segments. This arrangement is repeated throughout the annular arrayof inner shroud segments.

[0015] While the diffuser recesses are shown to be of rectangular shape,the invention is not limited to any particular shape so long as thecooling air is sufficiently diffused.

[0016] By diffusing the cooling air before the cooling air reaches thesegment end face, and as the cooling air discharged into the gap betweenadjacent segments, the effectiveness of the convection cooling holes isincreased.

[0017] The invention has been described primarily with respect to innershroud segments in the first and second stages of a gas turbine, but theinvention is applicable to any segmented shroud or seal where coolingand/or purge air is supplied to gaps between the segments.

[0018] While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. An inner shroud assembly for a turbinecomprising: a plurality of part-annular segments combining to form aninner, annular shroud adapted to surround rotating components of aturbine, each segment having a pair of end faces that are juxtaposedsimilar end faces on adjacent segments with gaps therebetween; at leastone convection cooling hole in the segment, opening along at least oneof said pair of end faces; said at least one cooling hole opening into adiffuser recess formed in said one of said pair of end faces fordiffusing the flow of cooling air into said gap.
 2. The inner shroud ofclaim 1 wherein said diffuser recess is substantially elongated inshape, with lengthwise surfaces on opposite sides of said at least onecooling hole tapering inwardly toward said cooling hole.
 3. The innershroud of claim 2 wherein a major one of said lengthwise surfacesextends downstream of said at least one cooling hole.
 4. The innershroud of claim 2 wherein said at least one convection cooling hole hasa diameter substantially equal to a width dimension of said diffuserrecess.
 5. The inner shroud of claim 1 wherein at least one additionalcooling hole opens along the other of said pair of end faces.
 6. Asegment for a turbine shroud assembly comprising: a segment body havinga sealing face and opposite end faces; and at least one convectioncooling hole extending through said segment body and opening into adiffuser recesses formed in a respective end face of said segment body.7. The segment of claim 6 wherein said diffuser recess is substantiallyrectangular in shape, with lengthwise surfaces on opposite sides of theconvection cooling hole tapering toward said convection cooling hole. 8.The segment of claim 7 wherein a major one of said lengthwise surfacesextends downstream of said convection cooling hole.
 9. The segment ofclaim 7 wherein said convection cooling hole has a diametersubstantially equal to a width dimension of said diffuser recess.
 10. Amethod of purging cooling air into gaps between adjacent part annularsegments in a turbine shroud assembly comprising: a) supplying coolingair through one or more cooling holes formed in each segment, eachcooling hole opening along an end face of the segment; and b) diffusingthe cooling air before it reaches the end face of each said segment.